Merge branch 'ap-namespace-members-assoc-indexes' into 'master'

Add index for member_namespace and related columns

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/107304



Merged-by: Adam Hegyi <ahegyi@gitlab.com>
Approved-by: Jon Jenkins <jjenkins@gitlab.com>
Approved-by: Adam Hegyi <ahegyi@gitlab.com>
Co-authored-by: Alex Pooley <apooley@gitlab.com>